Industrial control systems, process control systems, distributed control systems and the like in process industries often comprise both hard wired data networks and wireless data networks. Process industries can include branches of industry such as pulp and paper, pharmaceuticals, food production, oil and gas extraction, production, processing and the like. Wireless sensor networks are used to communicate measurements and some control data between wireless field devices such as sensors and the industrial control system. Wireless sensors are most often battery powered.
Service life for a battery-powered wireless sensor depends on power use. Service life for a wireless sensor network also depends therefore on power use by individual wireless sensors. The radio receiver/transmitter of a wireless sensor typically consumes most power while sending a transmission, and power while listening for transmissions, and almost no power during an inactive state. Conventionally wireless sensors in a WSN are configured to use little or no energy during inactive periods, also called a sleep state, conserving energy for a limited number of periods for listening for signals and/or for transmitting a signal.
An industrial installation may contain hundreds or thousands of tiny electronic devices, able to sense the environment, compute simple tasks, communicate with each other, and form larger wireless mesh sensor networks (WSN). Information gathered by the sensors (e.g. temperature, humidity etc.) is transmitted in a multi hop fashion via direct neighbors (mesh network) to a control system. With methods such as self configuration and self organization the network reacts to node failures and disconnected nodes due to exhausted battery energy.
Due to the required small size of nodes as well as the strongly constrained battery capacity one major requirement in WSNs is to distribute the networks services in an efficient manner. The long-term strategy of that is to extend the lifetime of the network to a maximum. In more detail the overall sensor network services need to be kept up as long as possible with the same high reliability and expected determinism.
WSNs must provide a variety of discrete services with different resource requirements. Moreover different services have also a different consumption of battery energy, meaning there are very high energy consuming tasks and less energy consuming tasks. Also the position of the nodes has influence on this energy consumption, whereas a node in the middle of a network, and many neighbours, with an aggregation functionality will certainly consume more power than a node with an aggregation role with only few neighbours at the border. Some functionality needs only be performed by a subset of nodes at any specific time. Such functionality can be for instance aggregation (aggregator service needed), cluster routing (gateway service needed), localization (reference nodes with known position needed). In the end the number of different roles needed can vary depending on the application. We define such subsets of node functionalities as roles, and the nodes performing the roles will be called role nodes.
The energy demand of a role varies significantly for different roles. Typically, the role nodes consume incomparably more energy than the other sensor nodes due to more complex calculations and higher communication efforts needed. The role nodes must provide high availability and cannot sleep as long and as frequently as the other nodes. This makes them more vulnerable to battery exhaustion. A rapid exhaustion of role nodes quickly limits or blocks the operation and functionality of the whole network.
A patent application US20090111532 entitled Method and system for power-based control of an ad hoc wireless communications network, and assigned to Nokia Corporation, describes a method, system and program code to implement a wireless network having a plurality of devices in which one of the devices coordinates wireless communications between the devices. The description describes node condition in terms of battery level and aim to coordinate devices to optimize for communication across a network. Application US20050059420, same title, same assignee, also describes coordination in a network relative to node power level.
A patent U.S. Pat. No. 6,901,275, entitled Communication system, and communication device and communication method for use in the communication system, assigned to Toshiba Corp., describes a system aimed at preventing (the network) from concentrating communication on one terminal, thereby avoiding an increase in power consumption and thereby prolonging the network configuration time when forming a network by a plurality of devices. However, the consideration of network life is limited to a parameter for node battery power and the network structure is limited to the situation of a single Master with many slaves.
WO2008/141719, entitled Energy-driven cluster aggregation point re-election in a wireless sensor network, assigned to University College Dublin, describes a sensor network comprising a plurality of nodes arranged to communicate wirelessly with one another, at least some of the nodes being arranged to operate as an aggregation point for the network, in which the aggregation point communicates data between other nodes of the network and externally of the network. However only one function or role, that of data aggregation, is considered here and the operative extension of network lifetime is limited to being based on node battery power alone.
Patent application US20090141653, entitled Enhancement of node connectivity in a wireless communications network with changing topology via adaptive role changing, assigned to BAE Systems Information, describes a process and system for enhancing connectivity among nodes of a wireless communications network by adapting to changes in the network topology. Nodes of the network are configured to operate according to either (i) an ad hoc protocol wherein a given node assumes a role of a mesh node capable of connecting with other like-configured nodes, or (ii) a point-to-multipoint protocol wherein the given node assumes a role of either a base station, or a subscriber station being served by another node which is assuming the role of a base station. A determination is made as to whether each node should operate according to the ad hoc protocol or the point-to-multipoint protocol, in order to maintain an optimum state of connectivity among all nodes of the network. The roles described are only mesh node, base station etc., so they are limited to network properties.
U.S. 2005/033816 A1 discloses a terminal device and method for use in a media access communication system. Terminal devices store statistical information related to interference from an external communication system, and notify the stored statistical information to a master station. The master station is arranged to determine if one of the terminal devices is a candidate station for a master station capability handover destination based collected statistical information.
U.S. 2005/059420 A1 discloses a method and system for implementing a wireless network having a plurality of devices in which one of the devices coordinates wireless communication between the devices. The method and system evaluates device parameters of one or more of the plurality of devices, and determines a coordinator from the plurality of devices based on at least the available power source characteristics such as an available power source capacity, for one or more of the plurality of devices, wherein the coordinator is adapted to coordinate wireless communication between the devices in the wireless network.
EP 2 134 041 A1 discloses a wireless sensor network having a plurality of mobile sensor nodes. In the wireless sensor network a sink is provided and re-positioned as required by assigning the role of sink to one of the mobile sensors at a time.
However, the lifetime of a wireless network may also be affected by factors other than a power level of a node battery. When one of certain other operating conditions of one or more wireless nodes falls below an operating threshold, forming what is described here as a bad condition such as; bit error rate (BER), low memory availability, imprecise position, reduced available bandwidth, incomplete or unsuccessfully finished self test, un-validated node (in terms of security), bad location, high EMI noise in the environment, old software revision, bad connectivity (too few neighbouring nodes) bad or deteriorated antenna direction, then the maintenance of the wireless network may be compromised.
There are generally many different wireless protocols in use in industry. This includes proprietary protocols, open protocols and networks with more than one type of protocol operating in the same broadcast/reception area. Such protocols include for example Bluetooth and ZigBee. Two other examples of a wireless standard in use in industry are called ISA100 also including version ISA 100.11a, for wireless sensing in industrial automation applications, and WirelessHART. WirelessHART is a standard that was developed to be compatible with older HART standards for communication between industrial devices.